Soil Temperatures Key to Corn Planting
Everyone views risk differently. Some individuals are more concerned with the level or severity of consequences associated with a risky action while others focus more on the likelihood of a negative consequence arising from a specific action. In order for something to be considered risky, it must have a level of uncertainty to it. When we think of planting our crops, the weather is our unknown variable. As a farmer or gardener, you get to choose when and what to plant, but the temperature and rainfall are out of our control.
For Ohio, the general recommendation for planting corn is in late April to early May. In a year with mild to warmer temperatures in April and May, planting earlier means a higher yield potential. The tradeoff is that an earlier planting could experience a hard freeze after emergence or more likely, the seed will sit in the ground if the soil temperature does not stay at or above 50 degrees. Seed that sits in the ground for a long time is just waiting to get damaged by insects, wildlife, or possibly rot.
While 50 degrees is the soil temperature needed for corn to germinate, and our 2” soil temperature was at 54.6 degrees on April 8th in Wooster, just be aware that soil temperatures, especially at a shallow depth, change quite a bit.
I looked back at the past week’s temperatures from OARDC’s weather website to check the variability. On April 1st, the 2” soil temperature was only 46. By the 3rd, it had dropped down to 43 and then went back up to 46 the next day. The point is, even if the soil temperature today is over 50, it only takes a couple more days for that 2” soil profile to move back below 50 degrees and delay plant emergence.
Every year, there are risk takers though. Some years, they are the neighbor with the nicest corn around and it’s a foot taller than anyone else’s for over a month. Other years, they are out re-planting while everyone else is planting for the first time. The highest yields may come by pushing the envelope, but the greatest costs also exist in the same planting timeframe. It is a decision that each operation must make, hopefully after weighing the potential costs and benefits.
Newly emerged corn can be killed when air temperatures are maintained at 28 degrees or less for several hours, as noted in a University of Kentucky article on frost damage to young corn. With hard freeze damage, it usually takes 3-5 days before it is evident if the plants will recover or if a replant will be needed. Be aware, that crop insurance companies determine the earliest planting date that they will offer coverage for should the crop suffer damage!
Soybeans are less likely to be damaged by cold weather due to their later average planting date. It still may be beneficial to have an idea of the forecast in case of a potential for cold snap. Soybeans need a soil temperature of 54 degrees to germinate. Again, remember that at shallow depths, the soil temperature can change several degrees in one day.
Caution would suggest waiting until soil temperatures (including those at lower depths) are above the minimal germination temperature for either field crop for several days along with a positive projected forecast. This should be done avoiding waiting too late in the season at which point yield potential begins to decline due to a shorter growing season.
Like most things in life, there are tradeoffs and some level of risk. It is up to each grower to make the decision of when to plant.
Matthew Nussbaum is an OSU Extension Agriculture and Natural Resources Program Assistant and may be reached at 330-264-8722.
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